Weight. The wings hold up the plane, not the body. For a demonstration, put something hard yet flexible over a gap between two desks or something. Push down on the middle of the bridge section. Notice that the edges of the thing barely move, while the middle flexs up and down. On take off, the wings are lifting off, while the fuselage sits like a brick. The wingtips stay steady, while the fuselage stays where it is until the wings pull it up. In the meantime, the difference between the wings (lots of lift) and fuselage (very,very little if any) is increasing, hence the bending.
If you want to fully understand the principle, watch a B52 take off. It does not rotate. Its mighty wings "flex" and the fuselage simply lifts into the air in a horisontal attitude.
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Actually, the B-52 does not rotate because of the incidence of the wing at the wing root. The wing root incidence is large on the B-52, which means the wing has a higher angle of attack, and therefore doesn't need to "rotate" to take off.
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Yes. The wing flexing is the point in which the force of lift is greater than the weight than the plane, and then it takes off. The wings have to bear the weight of the whole plane. Good question IslipWN
Though we understand what CitationJet is saying, there is a difference between the angle of attack and the angle of incidence. The angle of incidence is the angle between the wing chord and a line parallel to the longitudinal axis of the airplane. The angle of attack is the angle between the wing chord and the relative wind.
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Actually, the B-52 does not rotate because of the incidence of the wing at the wing root. The wing root incidence is large on the B-52, which means the wing has a higher angle of attack, and therefore doesn't need to "rotate" to take off
And that is also why B-52's tend to fly with their nose pointed at the ground........seriously.
A wing is there to produce lift. When a wing isn't producing lift, only gravity effects it forcing it down. During takeoff lift is produced, and at a certian point enough is produced the airplane can take-off. But before that point is reached the airplane's wing is producing lift. This lift forces the wing up. The struture takes this upward load and reacts up moving upward itself.
A lot of aircraft with multiple wing tanks will have you use the inboard tanks first and then use the outboard ones, this helps keep the bending forces to a minimum.
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The wings are designed to flex during flight. The wings probably flex more today because wings are now made from lighter, thinner, stronger material that can withstand a fair amount of bending.
Also, B747-400 has a longer wing than a B747-200. Also, A340/330 and B777 have very long wingspan:
Just as a note on the B52. On the Military Av/space forum is a link to a a B52 crash. Just imagine that guy as a flight instructor.It was about thirty topics down on the list. Look for "Spectacular crash of B52".
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Thanks for the input's on newer aircraft wing flexing. I knew about
modern alloys being stronger, but I forgot it in my first post.
Watching the wingtips/winglets on a 744 flex upward during takeoff is one of my favorite things.For a fully loaded 744, it seems the flex is in the 10 to 12 foot range. Does anyone know the actual flex on a 744?
I don't know how far they flex, just that when a 777 I was on took off, I thought the wings were going to snap they flex so far! Seriously... it's quite a sight in heavy turbulence too when they bounce around like mad! I guess it's the skyscraper principle - they flex to go with the stress, otherwise they'd crack!
The total wing flex on a Boeing 744 is 29 ft from top of the deflection to the bottom. I have an actual video of the destructive testing on the 744. When the wing spars finally fail, it sounds like a bomb going off.
I also think that while the planes rotate the wings do face the major direction of the plane not with the leading edge, but more with the lower surface.
So I guess the air resistance adds to te weight of the plane itself, same during landing. It is less while cruising, because there is "only" the weight...
Actually JadedMonkeys, not that I have gotten a nap and thought about it.
The whole reason why Boeing put that large angle of incidence on the aircraft to begin with was because of the landing gear design and it's inablity to handle rotation, either at T/O or landing.
About the nose down attitude in flight I mentioned, the USAF has a great publicity shot of a B-1,B-2 and B-52 in formation. You can really tell the differences in attitude to maintain level flight. This is about the best shot of the effect I could find here. The B-1 and the B-52 are flying in formation, so same airspeed and such, Look at how much farther nose down the B-52 has to be to match the B-1
The inablity to rotate was handled by other aircraft desingers, including Boeing usually by having a much longer forward strut then aft one, which gave most of them a distinctive nose up appearance when parked.
If you want to see the destructive testing on the B777, just get a documentry of the B777 and you'll see how powerful that was. It was fun to watch. I think you can order it off of Boeings website or off of A&E's website.
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